基于永磁风电机组变流器孤网频率控制研究

发布时间：2018-04-02 09:39

本文选题：孤岛电网　切入点：频率稳定　出处：《沈阳工业大学》2017年硕士论文

【摘要】：微电网是一种将分布式电源、负荷、储能装置、变流器以及监控保护装置有机整合在一起的小型发配电系统。微电网解决了分散式并网难的问题,提升了风电的利用率。随着风电渗透率的增加,微网频率波动进一步加剧,孤网模式下频率波动尤为严重。本文针对孤网中负荷增加与风速波动引起频率跌落及小幅度振荡问题展开研究,通过改进变流器的控制策略解决孤岛电网低频震荡问题。首先,建立永磁发电机和变流器的数学模型,分析永磁风电机组有功功率控制特点,采用矢量控制策略实现风电机组有功、无功解耦控制,为后续研究提供理论基础。其次,分析孤网功率平衡特性,针对孤网中转动惯量控制策略出现频率二次跌落问题提出降载荷控制策略。在低风速区,风电机组追踪次优功率曲线超速减载运行,保留有功备用余量为风电机组参与孤岛电网调频做准备。在高风速区,协调变桨距角控制策略与降载荷控制策略,在确保风电机组稳定运行的前提下,保留充足的有功功率备用余量支撑孤岛电网频率的稳定性。所提降载荷控制策略,在高、低风速区均解决频率二次跌落问题。再次,针对单一降载荷控制策略不能有效解决低频震荡问题,本文提出协调机侧分段减载与网侧模糊下垂的联合控制策略。分段减载控制策略在分析不同降载荷系数功频特性的基础,对全风速范围进行划分,在不同风速区间确定合适的降载系数,解决单一降载荷控制策略下有功功率备用余量不足的问题,增强风电机组对孤岛电网频率稳定性的支撑作用。网侧模糊下垂控制策略,通过设计模糊控制器和模糊规则,建立了孤岛电网频率偏差、频率变化率与风电机组补偿功率间的联系,优化了变流器的输入输出功率,有效抑制孤网频率骤降,解决低频震荡问题。最后,在Matlab/Simulink仿真环境中,搭建不同控制策略下风电机组参与孤岛电网调频时的仿真模型,进行仿真验证。结果表明联合控制策略下,永磁风电机组的运行状态最稳定,孤岛电网频率波动最小。在仿真的基础上,通过实验进一步验证联合控制策略可行性和有效性。
[Abstract]:Microgrid is a small power generation and distribution system that integrates distributed power sources, loads, energy storage devices, converters, and monitoring and protection devices.Microgrid solves the difficult problem of decentralized grid connection and improves the utilization rate of wind power.With the increase of wind power permeability, the frequency fluctuation of microgrid is further aggravated, especially in the isolated grid mode.In this paper, the problem of frequency drop and small amplitude oscillation caused by load increase and wind speed fluctuation in isolated network is studied, and the problem of low frequency oscillation in isolated island power network is solved by improving the control strategy of converter.Firstly, the mathematical model of permanent magnet generator and converter is established, and the characteristics of active power control of permanent magnet wind turbine are analyzed. The vector control strategy is used to realize the decoupling control of active power and reactive power of wind turbine, which provides a theoretical basis for further research.Secondly, the power balance characteristics of the isolated network are analyzed, and a load reduction control strategy is proposed for the frequency secondary drop of the moment of inertia control strategy in the isolated network.In the low wind speed area, wind turbines track the sub-optimal power curve to overspeed and reduce the load, and reserve the active power reserve for the wind turbine to participate in the frequency modulation of the isolated island power network.In the high wind speed region, the variable pitch angle control strategy and the load reduction control strategy are coordinated. Under the premise of ensuring the stable operation of the wind turbine, sufficient active power reserve is reserved to support the stability of the isolated island power network frequency.The proposed load control strategy solves the problem of frequency secondary drop in high and low wind speed regions.Thirdly, since a single load reduction control strategy can not effectively solve the problem of low frequency oscillation, this paper proposes a joint control strategy of coordinating segment load reduction on the side of the machine and fuzzy droop on the grid side.The piecewise load reduction control strategy is based on analyzing the power and frequency characteristics of different load reduction coefficients, dividing the whole wind speed range, and determining the appropriate load reduction coefficients in different wind speed ranges.To solve the problem of insufficient spare allowance of active power under a single load reduction control strategy, and to enhance the support function of wind turbine to the frequency stability of isolated island power network.By designing fuzzy controller and fuzzy rules, the relationship among frequency deviation, frequency change rate and compensation power of wind turbine is established, and the input and output power of converter is optimized.Effectively restrain the frequency drop of the isolated network and solve the problem of low frequency oscillation.Finally, in the Matlab/Simulink simulation environment, the simulation model of wind turbine participating in frequency modulation of isolated island power network is built under different control strategies, and the simulation results are verified.The results show that the operation state of permanent magnet wind turbine is the most stable and the frequency fluctuation of isolated island power network is minimum under the joint control strategy.On the basis of simulation, the feasibility and effectiveness of the joint control strategy are further verified by experiments.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM712;TM614

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